( 168 ) 

 WIND AND FLIGHT. 



BY 



F. W. HEADLEY, m.a., m.b.o.u. 



Part III. 



{Continued from page 146.) 



Soaring. 



Various theories are held about soaring-. Those who are 

 I)rej)ared to treat mathematics and mathematicians with 

 contempt maintain that a uniform horizontal wind is 

 capable of lifting a bird when he faces it. But as a fact 

 it will not help him at all unless he offers resistance, 

 unless, in fact, he has inertia. If the wind were hori- 

 zontal but its successive currents of different velocity, 

 it is in theory possible that a bird might gain the required 

 inertia by passing from a slowly moving current into a 

 rapid one, as the lark does in rising. Possibly a bird may 

 make use of eddies ; he may pass from a part of an eddy 

 where the air moves but slowly into a region of rapid 

 movement. Thus he would not be like a mere floating 

 balloon, but, resisting the wind, would be supported and, 

 possibly, lifted by it. Soaring, then, is theoretically 

 possible with a horizontal wind that is not uniform in 

 velocity. But though theoretically possible it seems 

 unlikely that it is actually effected in this way. 



Let us first consider what goes on in regions where we 

 can investigate facts. In the lower strata of air we find 

 birds rising and advancing by means of ujs-currents which 

 they find so effectual that they dispense with all beating 

 of the wings. Gulls, hanging over the stern of a steamer, 

 their wings held rigid, keep pace with the vessel which is 

 travelling, say, fifteen knots an hour, and it is impossible 



